1. Field of the Invention
The present invention relates to a liquid crystal display device and a method of fabricating the same, and more particularly, to a driving circuit integrated type liquid crystal display device, in which a large area panel can be manufactured by realizing a low resistance wiring, and a method of fabricating the same.
2. Discussion of the Related Art
Recently, displays are considered to be more and more important as a visual information transmission media. In order to occupy a major position in the future, the display has to satisfy a low power consumption characteristic, a thin and light characteristic, and a high picture quality characteristic. Because a liquid crystal display (LCD) device (a popular type of flat panel display (FPD)) not only satisfies these requirements but also allows for mass production. Thus, various kinds of new products using the LCD device are being developed, and the LCD device has become the leading replacement of the existing cathode ray tube (CRT) technology.
Generally, a liquid crystal display device is a display device for displaying desired images by supplying data signals corresponding to image information to liquid crystal cells arranged in a matrix, respectively, and controlling the light transmittance of the liquid crystal cells.
The Active Matrix (AM) method, the primary driving method for the liquid crystal display device, is a method that drives liquid crystal in a pixel portion using an amorphous silicon thin film transistor (a-Si TFT) as a switching device.
The concept of amorphous silicon thin film transistor technology was established by LeComber, United Kingdom et al. in 1979, and put into practical use as a 3-inch liquid crystal portable television in 1986. Recently, a large area thin film transistor liquid crystal display devices larger than 50 inches have been developed. In particular, the amorphous silicon thin film transistor is actively used since a glass substrate of a low price is useable because a low temperature process is available.
However, there are limitations on using the amorphous silicon thin film transistor for a peripheral circuit requiring high speed operation greater than 1 MHz by an electric mobility of 0 to 1 cm2/Vsec of the amorphous silicon thin film transistor. Accordingly, the study of integrating both the pixel portion and the driving circuit portion on a glass substrate using polycrystalline silicon (poly-Si) thin film transistors having a field effect mobility greater than amorphous silicon thin film transistors is being actively pursued.
The polycrystalline silicon thin film transistor technology has been adapted to a small-size module of a camcorder or the like since the liquid crystal display color television was developed in 1982. It has an advantage that a driving circuit can be manufacture directly on a substrate because of a low photosensitivity and a high field effect mobility.
An increase in the mobility can improve the operational frequency of the driving circuit portion for determining the number of driving pixels, and this makes it easier to achieve the high definition of a display device. Further, a picture quality improvement can be anticipated because the distortion of a transmission signal is reduced by a reduction in the charging time of a signal voltage of the pixel portion.
Furthermore, the polycrystalline silicon thin film transistor has an advantage that power consumption can be reduced because it can be driven at less than 10V as compared to the amorphous silicon thin film transistor having a high driving voltage of 0 to 25V.
Hereinafter, a structure of a liquid crystal display device will be described in detail with reference to the accompanying drawings.
FIG. 1 is a plan view schematically illustrating a structure of a related art liquid crystal display device, in which a driving circuit integrated type liquid crystal display device having a driving circuit portion integrated on an array substrate is illustrated.
As illustrated therein, the liquid crystal display device largely comprises a color filter substrate 5, an array substrate 10, and a liquid crystal layer (not illustrated) formed between the color filter substrate 5 and the array substrate 10.
The array substrate 10 includes a pixel portion 35, an image display region in which unit pixels are arranged in a matrix, and a driving circuit portion 30 located at the periphery of the pixel portion 35 and having of a data driving circuit portion 31 and a gate driving circuit portion 32.
Though not illustrated in the drawings, the pixel portion 35 of the array substrate 10 includes a plurality of gate lines and a plurality of data lines that define a plurality of pixel regions by being arranged vertically and horizontally on the substrate 10, a plurality of thin film transistors serving as switching devices formed at intersections of the gate lines and the data lines and a plurality of pixel electrodes formed in the pixel regions.
The thin film transistor is a kind of field effect transistor (FET) serving as a switching device for applying and intercepting a signal voltage to and from the pixel electrodes which controls the flow of an electrical current by an electric field.
The driving circuit portion 30 of the array substrate 10 is located at the periphery of the pixel portion 35 of the array substrate 10 protruded on the color filter substrate 50. The data driving portion 31 is located at a long side of the protruded array substrate 10, and the gate driving circuit portion 32 is located at a short side of the protruded array substrate 10.
The data driving circuit portion 31 and the gate driving circuit portion 32 use a thin film transistor of a CMOS (Complementary Metal Oxide Semiconductor) structure, which is an inverter, in order to properly output an input signal.
For reference, the CMOS is a kind of integrated circuit of a MOS structure used for driving circuit portion thin film transistors that require high speed signal processing. The CMOS requires both N channel thin film transistors and P channel thin film transistors, and its speed and density characteristics exhibit an intermediate form between a NMOS and a PMOS.
The gate driving circuit portion 32 and the data driving circuit portion 31 are an apparatus for supplying scanning signals and data signals to the pixel electrodes via the gate lines and data lines, respectively. They are connected to an external signal input terminal (not illustrated) and thus serve to control an external signal coming through the external signal input terminal and output it to the pixel electrodes.
A color filter (not illustrated) for implementing colors and a common electrode facing the pixel electrodes formed on the array substrate 10 are formed at the pixel portion 35 of the color filter substrate 5.
The color filter substrate 5 and array substrate 10 constructed as above are provided with a cell gap therebetween so as to be regularly spaced apart from each other, and face each other and are attached by a seal pattern (not illustrated) formed on an outer edge of the pixel portion 35, thereby forming a unit liquid crystal display panel. The attachment of the two substrates 5 and 10 is formed through an attachment key (not illustrated) formed at the color filter substrate 30 or the array substrate 10.
Gate wiring and data wiring are means for applying scanning signals and data signals, respectively, and required to suppress a signal delay and disconnection.
In particular, material used for the wirings should have a specific resistance less than a predetermined level, should not be easily oxidized, and should not be easily broken in the fabricating process.
However, current technologies are unable to efficiently implementa large area liquid crystal display panel requiring a low resistance wiring.